1. Field of the Invention.
This invention pertains generally to the field of machines for assembling cartons, and more particularly to apparatus which applies plastic film panels to carton blanks which have cut-out "windows" formed in them which are covered by the film panels.
2. Description of the Prior Art
Tissue dispensing cartons often have a cut-out opening in them which is covered by plastic film. A cut or cut-out portion of the film allows the user to reach through and pull out a single tissue at a time. The cut plastic window has the advantage of allowing the user to see the contents of the carton, while providing a resilient and flexible material which can hold the next tissue to be dispensed in a position above the top of the box so that it is easily reached by the user.
The plastic film is typically provided from a continuous roll with cuts or slits being formed in spaced relation in a continuous sheet drawn from the roll. After cutting, the continuous sheet of film is then delivered to apparatus which cuts the sheet to form appropriately sized panels and then delivers the panels to a position where they are adhered to the carton blanks. However, thin plastic films are difficult to handle or rewind into a roll after cutting of slits or openings without stretching, buckling or tearing of the film. As an alternative to cutting the film first, the uncut film panels have been applied to the carton blanks and the completed unit has then been fed to a mechanism which makes the appropriate cut in the plastic window. Two separate operations are again required, the adhering of appropriately sized panels to the carton blank and the subsequent cutting of the window in the blank.
A typical windowing machine includes a large vacuum drum which has a perforated surface. The proper width of the plastic film is usually supplied from a large roll of film, is cut to length by a rotary knife cylinder which mates with an anvil on the vacuum drum, and is held in position by vacuum draw through the drum perforations as a result of vacuum applied to the interior of the drum. A timed feeding device delivers flat blanks or cartons through a glue application station where adhesive is applied in a pre-determined pattern generally surrounding the cut-out opening or window in the carton. The carton is delivered to a nip formed between the vacuum drum and a back-up nip roll such that the precut plastic film panel registers to cover the cut-out opening in the blank. An internal manifold arrangement within the drum releases the vacuum from the film as it passes out of the nip, thereby allowing the film to remain adhered to the blank without interference.